1. Field of the Disclosure
The present invention relates to a mounting ring. It also relates to an assembly having a housing with a bore therein and a shaft or bearing (hereinafter the term “shaft” encompasses a bearing) received in the bore and connected thereto to be held in the bore by such a mounting ring.
2. Description of the Related Art
It is known to connect together a housing and a shaft received in a bore of the housing by a mounting ring in the form of a tolerance ring. The tolerance ring may be used to hold the shaft in place in the bore, or it may act as a force limiter to permit torque to be transmitted between the shaft and the housing. Tolerance rings are used, for example, to transmit torque, provided that torque does not exceed some predetermined value. The use of a tolerance ring permits minor variations in the diameter of the shaft and the bore to be accommodated without affecting the housing and shaft interconnection.
Conventional tolerance rings generally comprise a band of resilient material, for example a metal such as spring steel, the ends of which are brought together to form a band. A strip of projections extend radially outwards from the band, or radially inwards towards the centre of the band. Usually, the projections are formations, possibly regular formations, such as corrugations, ridges, waves or fingers.
When the ring is located in the annular space between, for example, the outer surface of the outer part of a bearing and a bore in a housing in which the bearing is located, the projections are compressed. Each projection acts as a spring and exerts a radial force against the bearing and the surface of the bore, providing an interference fit between the bearing and the housing. Rotation of the housing or the outer part of the bearing will produce similar rotation in the other of the bearing or the housing, as torque is transmitted by the tolerance ring. Likewise, linear movement of the housing or the outer part of the bearing will produce similar linear movement in the other of the bearing or the housing, as the linear force is transmitted by the ring.
If forces (rotational or linear) are applied to one or both of the outer part of the bearing and the housing, such that the resultant force between the mating components is higher than a certain threshold value, the bearing or housing will move relative to one another, i.e. they will slip. In this application, this threshold value is referred to as the “slip force” of the bearing, housing and tolerance ring.
Although tolerance rings usually comprise a strip of resilient material that is curved to allow the easy formation of a ring by overlapping the ends of the strip, they may also be manufactured as an annular band.
Tolerance rings can thus provide torque transfer or torque limiting functions, provide axial retention or axial sliding force control by providing an interference fit as the projections are compressed between the mating components of the assembly.
A known tolerance ring 1 is shown in FIG. 1. The tolerance ring 1 comprises a band 11 of spring steel, the ends 12, 13 of which are brought together to form a band. A strip of projections 14 extend radially inwards from the inner circumferential surface 17 of the band. The projections 14 are regular corrugated formations. The strip of projections 14 is axially flanked by annular regions 15, 16 of the band of resilient material 11 that have no formations.
FIG. 2 shows the known tolerance ring 1 of FIG. 1 in use in an electric motor. When the components shown in FIG. 2 are assembled, the electric motor comprises a rotor 6 mounted on a shaft 5 in a housing 3. The shaft 5 passes through bearings 2, tolerance rings 1, wavy washers 4 (discussed below), and end caps 7 of the motor. On assembling the motor, the tolerance rings 1 are located in the housing 3, and then each bearing 2 is pressed into one of the tolerance rings 1 in the housing 3 to compress the projections 14 of the tolerance ring 1, as described above, to retain each of the bearings 2 relative to the housing 3, without the need for tight machining tolerances or glue.
A problem with known assemblies of a bearing, housing and tolerance ring, such as in the electric motor of FIG. 2, is that, if the assembly gets hot, the housing may expand thereby increasing the annular space between the housing and the outer part of the bearing. When this happens, the bearing may be permitted to move axially relative to the housing, and the races of the bearing may be permitted to move axially relative to each other (i.e. rattle), which can lead to excessive wear between the balls of the bearing and the races, and also reduced NVH (noise, vibration and harshness) performance. In order to compensate for this, it is known to use “wavy washers” adjacent to bearings, to pre-load the bearings. Pre-loading is the application of a controlled axial load across a pair of bearings to force the rolling elements to assume a contact angle to remove free internal clearances, i.e. to cushion or prevent axial movement of parts of the bearing relative to each other.
A “wavy washer” is a piece of resilient material, such as spring steel, which takes a generally hoop or halo form. However, rather than being a plane hoop in a radial-circumferential plane, the material of a wavy washer can take the form of a wave, such that, with reference to the radial-circumferential plane, some portions of the hoop extend further axially from the plane than other portions. This formation enables the wavy washer to act as an axial spring.
A pair of known wavy washers 4 are shown in FIG. 2. When the components in the drawing are assembled, the faces 2a of the inner races 22 of the bearings 2 abut the faces 5a, 5b of the shaft 5, and the wavy washers 4 abut the axially opposite faces 2b of the outer races 23 of the bearings 2. The bearings are then said to be pre-loaded.
FIG. 3 shows a cross section through the left hand one of the pair of bearings 2 of FIG. 2, when the components in FIG. 2 are assembled. FIG. 3 demonstrates that the inner race 22 of the bearing 2 is urged leftwards (by the shaft 5), and the outer race 23 of the bearing 2 is urged rightwards (by the resilient wavy washer 4). Thus, even if the assembly gets hot and the tolerance ring 1 fails to provide a sufficient interference fit between the bearing 2 and the housing 3 to prevent relative axial movement of the outer race 23 and the housing 3, and thus relative axial movement of races 22, 23 of the bearing 2, the wavy washer 4 forces the rolling elements to assume a contact angle “a” to avoid free internal clearances.
While tolerance rings and wavy washers have many beneficial attributes, they can be time-consuming and awkward to fit in an assembly.